(1) Field of the Invention
The present invention relates to a television signal processing circuit, and more specifically to a television signal processing circuit that is adapted for processing not only those standard color television signals that are transmitted from the broadcasting stations but also those television signals that are at least partly different in time and phase from the above standard color television signals.
(2) Description of the Prior Art
Owing to the development in the semiconductor integrated circuit technology, delay means (such as frame memory or field memory) having a delay time equal to, or longer than, the vertical scanning period of a television signal has been realized in a small size and at a reduced cost. By utilizing this means, a variety of signal processing circuits have been put into practice.
According to known signal processing systems, color television signals are divided into signals and color difference signals by using a frame memory, or television signals under the interlaced scanning, are interpolated among the scanning lines using a field memory and are converted into successive scanned signals. With the above-mentioned signal processing circuit employing a video memory such as field memory or frame memory having a delay time that is nearly equal to the vertical scanning period of a television signal or nearly equal to an integer number of times thereof, there are obtained output signals of a high quality when the input television signals conform to those of the signals of a standard color television system. In processing the output signals of video tape recorders for domestic use that are now widely used, however, it is difficult to properly process the signals by utilizing the delay of field period or frame period, since these signals are deviated from the standard color television signals. For instance, these signals have large jitters and their color subcarrier frequency is not an integer and a half multiple of the horizontal scanning frequency. In separating a composite signal into a luminance and a color difference signal by using a frame memory, color subcarrier phase difference between frame periods must be 180 degrees. With the video tape recorders for domestic use, however, the signals are not so, and the signals are not properly separated into luminance signals and chrominance signals by inter-frame processing. In the scanning line interpolation using a field memory, furthermore, the field period does not remain constant and interpolation signals are not obtained correctly. Accordingly, if signals of a household video tape recorder are processed by a processing circuit which has such a video memory as a field memory or a frame memory, there are obtained only those signals that are very deteriorated.